The long-term objectives of this project are to understand the molecular basis of expression of the myotonic dystrophy (DM) locus in the human ocular lens and to provide a human genetic model for the formation of cataracts. Recent rapid advances in the molecular genetics of DM have narrowed the region about the locus of the responsible gene to about 300 kilobases in the q13.3 band of human chromosome 19. There is a very high likelihood that the DM gene and mutation(s) will be identified within the year. In this light, the proposed specific aims are highly feasible and very timely in planning studies of the cellular and molecular aspects of expression of the DM gene in the eye lens. The human ocular lens is the site of highly specific cataracts expressed in most DM patients and is a histologically simple structure that is amenable to molecular and cellular investigation of gene expression. The first specific aim is to characterize mRNA from the human lens for expression of the DM gene. The second specific aim is to identify the DM-encoded protein in human lenses. The third specific aim is to localize DM mRNA and protein to specific cellular and subcellular sites within the human lens. The fourth specific aim is to establish developmental patterns of expression of the DM gene in fetal and maturing human lenses. The fifth specific aim is to analyze cataractous lenses from DM patients for DM RNA and protein, their alteration by mutation, and their localization at cellular and subcellular levels. This specific aim although potentially important for understanding the mechanisms of cataract formation must be tentative because of the low frequency of DM patients in the lens clinic population combined with the currently conventional technique of lens removal, phacoemulsification, which destroys the integrity and morphology of the lens and dilutes lens material with washing solutions. The sixth specific aim is to characterize the DM-like gene of mice. The mouse studies will involve the molecular and cellular methods used in the human work and will offer the opportunity to study early developmental events and possibly establish an animal model for DM. This aim will necessarily continue past the initial program period. The accomplishment of the specific aims will provide important information about the biology of the human lenses that should be highly relevant to understanding the formation of cataracts in a well-defined human genetic disease.